Mauna Loa is inflating again
Oblique shaded-relief map of the five volcanoes
that built the Island of Hawai`i. Mauna Loa encompasses 51 percent
of the island's surface area; its most recent eruption was in
1984. Click for
Continuously recording GPS receivers were installed on the
summit and upper flanks of Mauna Loa in 1999 to
detect changes in shape of the volcano that
typically accompany underground movement of magma. The GPS
instruments allow such ground deformation to be tracked
continuously and also more accurately than was possible before.
Until May of this year, the new instruments showed what we
already knew from other surveying techniquesthe summit
caldera was slowly subsiding and shrinking.
But in late April to late May, centered on May 12 (Mother's
Day), the GPS receivers began
moving slightly in a different direction. Since May, the
instruments show that Mauna Loa's summit area is rising
slightly and the caldera is widening 5-6 cm per year.
What caused the abrupt change? Our computer models of the
moving GPS receivers suggest that the current ground motion
is the result of magma rising into a reservoir about 5 km
below the caldera. Only time will tell if this new trend will
continue in the coming months.
The nature of seismicity changed several months before each
of the latest two eruptions. Large increases
were obvious in both the numbers of earthquakes and the amount of energy
released by these earthquakes. That is a reasonable expectation
before the next eruption, though we must be cautious in saying
that such an increase must occur. For more